This invention relates in general to apparatus for collecting solar energy for use and, more particularly, to a solar energy collection panel in which solar energy is collected and directed to an energy absorbing tube.
A wide variety of solar energy collectors have been developed for heating fluids such as water, generating electricity, etc. Some are simple and passive, basically simply using a black plastic tube exposed to sunlight through which water is circulated to heat a swimming pool or the like. Photovoltaic panels convert sunlight energy directly into electrical energy. Others include mechanisms for moving a collector panel to track the sun, either manually or automatically, to improve collection efficiency. For heating water or other fluids, the sun tracking systems tend to have the highest efficiency.
Typical of prior sun tracking solar energy tracking systems are those described by Doundoulakis in U.S. Pat. No. 4,307,711 and Rogers in U.S. Pat. No. 3,929,121. In such collectors, a plurality of condensing lenses, which may be fresnel lenses, are focussed on spots on collector elements, such as fluid carrying tubes. The lenses and tubes are mounted in frames that are movable to keep the lens system pointed at the sun. The lens systems for focussing sunlight on small spots are complex and expensive to manufacture and are difficult to maintain precisely in focus on the collecting medium.
Other systems use concave mirrors of complex optical design, typically mounted on poles, for focussing sunlight on a centrally located receiver, such as is described by Clark in U.S. Pat. No. 4,192,289. Typically, these systems are used to boil a fluid, such as water, that is then passed to a steam powered electrical generator. These systems are large and complex. Maintaining alignment between the mirrors and the receiver is difficult.
Both the lens and mirror systems require a sun tracking system, such as those described by Smith in U.S. Pat. No. 4,179,612 and Hammons in U.S. Pat. No. 4,225,781. Difficulty is often encountered in maintaining accurate tracking and preventing flexing and distortion of the collection system during movement of large lens or mirror arrays.
Many solar energy collecting systems lose a large portion of the energy received to the atmosphere or support structures. Some lose energy almost as fast as it is collected. Complex and heavy thermal insulation systems are sometimes resorted to limit energy losses. These increase the cost of the system, make distortion of collector panels more likely and require heavy, sturdy tracking systems.
In order to provide the required rigidity and strength, many systems are very heavy and require on-site assembly from many different components. These intricate systems have continuing maintenance problems and are difficult to disassemble, even partially, for maintenance. Prior systems also have been susceptible to damage from severe weather conditions, vandalism, etc. and are difficult to repair or replace.
Thus, there is a continuing need for improved solar energy collection systems that are inexpensive, sturdy and simple to assemble, and which provide improved energy conversion through improved energy transfer efficiency and lower heat losses in the system.